Asphalt is in use in most places that vehicles are. Asphalt is durable, economical, and should last for many years. Asphalt will not last forever though, and some sections of asphalt may well deteriorate prematurely, leading to failure of surrounding portions if not addressed promptly. Common causes of premature failure in asphalt sections are excessive water flow, poor drainage, sinking of underlying ground, and oil, grease, gasoline, or chemical oxidation.
The United States alone spends roughly $16 billion USD annually on repair of existing roadways (calculated based on the Federal Highway Administration's Highway Statistical Series, for years 2004-2008). According to the American Association of State Highway and Transportation Officials, every $1 spent to keep a road in good condition avoids $6-14 needed later to rebuild the same road once it has deteriorated significantly (American Association of State Highway and Transportation Officials (AASHTO) and The Road Information Project. (2009). “Rough Roads Ahead: Fix Them Now or Pay for It Later.” http://roughroads.transportation.org/.)
To this end, many repair techniques have been developed, such as “throw-and-go” (placing fresh asphalt into a pothole or crack, with no further steps), “throw-and-roll” (similar to throw-and-go, but also includes an attempt to compact the fresh asphalt by driving over it with a vehicle), spray injection (requires customized vehicles and materials, involves spraying of asphalt mix through a nozzle and onto the existing asphalt to be repaired), edge seal (cutting the deteriorated pavement out, adding fresh asphalt, and compacting with vibratory rollers or the like), and infrared heating and repair. Of these, infrared heating and repair of damaged asphalt has many benefits, including seamless bonding of the patch to the surrounding asphalt, requiring only one trip to the site of the repair, less new asphalt being necessary to make a similar repair, fewer freeze/thaw issues occurring, and less potential for injury of workers, because there is no need for saw cutting, jack hammering, spraying of solvents, or the like.
Existing infrared asphalt repair apparatus are either of the ceramic blanket or metal ribbon variety. Ceramic blanket heaters typical of the prior art use LPG (Liquefied Petroleum Gas) to heat a ceramic blanket, which in turn radiates infrared energy. Metal ribbon heaters generally use a plurality of thin strips (ribbons) of metal that are placed in a channel, bent in a wave-like pattern, and welded every 6-12″. LPG is channeled through the orifices formed between the metal ribbons, and lit. This LPG then heats grids, typically made of nickel chromium, which radiate infrared energy into the pavement. Infrared heating is used instead of purely convective heating due to superior efficiency. By using infrared radiation, less heat is wasted heating up the surrounding air, because the infrared radiation travels through the air, losing little energy, before being absorbed by the asphalt. Infrared heating also provides quicker heating of sub-surface asphalt than purely convective heating. Because the actual heating is done through infrared radiation, rather than convective heating, the asphalt is evenly heated and softened throughout its depth. However, the current state of the art in infrared heating and repair of asphalt is not without its problems.
Ceramic blanket heaters will eventually need to have the ceramic blanket replaced at substantial cost, either due to normal use or because it has developed tears in the material. The efficiency of ceramic blanket heaters will also deteriorate because of a buildup of carbon and other combustion byproducts on the ceramic blanket over time.
Metal ribbon infrared asphalt heating and repair devices also suffer issues that prevent their widespread adoption, typically suffering from uneven and inconsistent heating, unreliable operation, high temperature operation (reduced durability), and high fuel usage. In particular, the sizes of the orifices created by bending and periodically welding metal ribbon material in a channel are inconsistent, in turn affecting the uniformity of heat given off by the device. This variation in orifice size and heat requires additional expenditure of fuel to achieve at least a minimum usage temperature throughout the heated region, and also allows for occasional large bursts of flame through these ribbons, referred to as flame-throughs, which can cause failure of the nickel chromium grids, as well as scorching of the asphalt. The higher than necessary operating temperature required because of the non-uniform output of these devices also considerably shortens the life of the nickel chromium material.
What is needed, therefore, are apparatus for infrared heating and repair of pavement that use less fuel, eliminate flame-through events, provide more uniform output, and are more robust than those of the prior art.